Hyperbaric breathing mixture

ABSTRACT

An oxygen component of suitable partial pressure for breathing is mixed with an inert component comprising carbon tetrafluoride (CF4), or a mixture of carbon tetrafluoride and helium (He), the inert components having a combined pressure depending upon the pressure of the environment in which breathing is to be sustained. The relative volume percentages of the CF4 and the He are adjusted to optimize certain properties of the breathing mixture to provide improvements over standard compressed air or helium-oxygen mixtures.

United States Patent Ormand et a1.

[ 51 July 11,1972

[54] HYPERBARIC BREATHING MIXTURE [72] Inventors: lh-ederick T. Ormand;Huey V. Auger,

both of Basking Ridge, N .J

[73] Assignee: Airco, lnc., New York, NY.

[22] Filed: April 6, 1970 [21] Appl. No.: 23,101

Related US. Application Data [63] Continuation of Ser. No. 687,426, Dec.4, 1967, abandoned.

[52] US. Cl ..424/366 [51] Int. Cl ..A6lk 13/00, A6lk 27/00 [58] Fieldof Search ..424/366; 252/372 [56] References Cited UNITED STATES PATENTS1,473,337 11/1923 Cooke ....424/366 1,644,363 10/1927 Yane et a1..424/366 OTHER PUBLICATIONS Merck Index, 7th Ed. Merck & Co., Rahway,N.J., 1960, p. 212

Rochsfort, Anal. Chem. Acta., 29, pp. 350- 357, 1963 Steeng et al.,J.Chem. Phys. 38, 1963, p. 1788 Booth, lnorg. Syn. 1 pp. 34-35, 1939Primary ExaminerHoward T. Mars Attorney-Edmund W. Bopp and H. HumeMathews [5 7] ABSTRACT 1 Claim, No Drawings SUMMARY OF THE INVENTION Theinvention relates to gaseous mixtures for breathing, particularly underpressure materially above normal atmospheric pressure, for example underwater, in deep sea diving, in hyperbaric surgical operations, etc.

The invention employs fluorine derivatives of hydrocarbon compoundscontaining only carbon and fluorineand most particularly carbontetrafluoride with or without another substantially inert component, forexample, helium in admixture with a partial pressure of oxygen suitablefor breathing, to form a hyperbaric breathing mixture.

The invention provides non-toxic breathing mixtures that are markedlyless narcotic under hyperbaric condition than mixtures in which theinert component is nitrogen as in compressed air. Furthermore, certainof the mixtures disclosed have acoustic properties similar to air,thereby avoiding the high-pitched voices caused by speaking whilebreathing mixtures in which the significant inert component is helium.Also, the mixtures disclosed have lower thermal conductivities thanthose in which the inert component is essentially helium, therebyreducing the bodily chilling experienced in breathing helium mixtures.We have found, further, that the mixtures disclosed herein can be usedat higher total pressures than mixtures in which the inert component isnitrogen. Furthermore, the tendency of helium to permeate the glassenvelopes of vacuum tubes or otherwise to permeate any sensitiveelectronic devices is'decreased by the admixture of carbon- DESCRIPTIONOF THE PREFERRED EMBODIMENTS Breathing mixtures in accordance with theinvention contain oxygen at any partial pressure suitable for breathing,usually in the range from about 2 to pounds per square inch andpreferably not exceeding 2 atmospheres, the latter limit serving toavoid deleterious physiological effects such as convulsions. To theoxygen there is added an inert gas or a mixture of inert gases selectedfrom halogen derivatives of hydrocarbon compounds,most particularlythose containing only fluorine and carbon, with or without an admixtureof helium, to bring the total pressure up to a desired value, which maybe materially in excess of normal atmospheric pressure.

Preferred mixtures in accordance with the invention are oxygen withcarbon tetrafluoride, and oxygen with carbon tetrafluoride-and helium.In the case of mixtures containing carbon tetrafluoride and helium, therelative volume proportions of carbon tetrafluoride and helium arepreferably adjusted to suit the particular use, with the object ofsecuring optimum over-all properties, for example, acoustic or thermalproperties similar to those of air, or reduction of the tendency ofhelium to permeate glass, vacuum tubes, or other sensitive electronicdevices.

We have tested our preferred mixtures as to their effects upon whitemice, in comparison with the effects on the mice of prior art mixturesof oxygen with nitrogen and of oxygen with helium alone. The tests weremade using oxygen at about normal atmospheric pressure, for conveniencein test procedure, since such pressure is safe for breathing and is wellbelow a level conducive to convulsions. Thetotal pressure of the inertcomponents, carbon tetrafluoride, helium and nitrogen, in each case wascarried as high as 150 pounds per square inch. However, there was noindication that 150 pounds per square inch is an upper limit of pressureat which the disclosed mixtures can safely be used.

Specific mixtures tested were (1) 14.7 p.s.i.a. oxygen with up to 150p.s.i.a. carbon tetrafluoride, and (2) 14.7 p.s.i.a. oxygen with 45p.s.i.a. carbon tetrafluoride and 105 p.s.i.a. helium. These mixtureswere breathed by white mice for test periods up to one hour with nomajor changes in the behavior of the mice and with no apparentdeleterious effects.

Reference mixtures (3) 14.7 p.s.i.a. oxygen with 150 p.s.i.a. nitrogen,and (4) 14.7 p.s.i.a. oxygen with 150 p.s.i.a. helium were breathed bythe mice in other tests used as controls.

It was found that the preferred mixtures (l) and (2) were less narcoticin their effects upon the mice than the mixture (3) containing nitrogen,and caused less chilling of the mice than the mixture (4) containinghelium as the sole inert component. With the mixtures l and (2) the micedid not appear to be near the threshold of narcosis, while there wasevidence of narcosis from the breathing of the mixture (3) containingnitrogen, so that it was clear that the carbon tetrafluoride mixtures(1) and (2) can be used at higher total pressures thannitrogen-containing mixtures.

In general, it was found that breathing mixtures containing carbontetrafluoride as an inert component are less toxic than mixturescontaining nitrogen, and that they reduce undesirable effects caused bybreathing helium without accompanying carbon tetrafluoride, such asrapid heat loss due to the high thermal conductivity of helium, heliumpermeation of sensitive electronic devices and glass as in the envelopesof vacuum tubes, and the high pitch of voice sounds due to the loweratomic weight of helium compared to air.

Breathing mixtures in which the inert component includes both carbontetrafluoride and helium are further preferred because by adjusting therelative proportions of the two inert gases, certain useful propertiesof the breathing mixture can be optimized or otherwise adjusted. We havefound that when the inert portion of the mixture consists of about 30volume percent carbon tetrafluoride and volume percent helium, theaverage molecular weight of the complete mixture is approximately thesame as for air. Accordingly, the acoustic properties of the mixture aresimilar to those of air, resulting in essentially normal voicecommunication without the high pitch effect usually observed withbreathing mixtures high in helium. The thermal conductivity of thepreferred breathing mixture, while somewhat higher than for air, islower than for helium. Consequently, the chilling effect upon the skin,observable with helium, is substantially avoided.

For a combined pressure of the inert gases of p.s.i.a., the preferredmixture of approximately 30 percent by volume of carbon tetrafluorideand 70 percent by volume of helium is equivalent to 45 p.s.i.a. carbontetrafluoride and 105 p.s.i.a. helium.

Proportioning of the ratio between carbon tetrafluoride and heliumcontent may be employed either to optimize a single parameter of thebreathing mixture or to optimize the effect of a combination of two ormore such parameters.

The following table shows standard and calculated values for certainpertinent parameters of carbon tetrafluoride, the mixture of 30 volumepercent carbon tetrafluoride 70 volume percent helium, straight helium,and air, respectively, at 20 C.

Viscosity (for laminar flow), grams per centimetersecond. x107 201x10119.61X Thermal conductivity calories per centimeter per second perdegree. 3.58X10' As shown by the Table, the average molecular weight,sonic velocity, viscosity for laminar flow, and heat capacity of the30-70 percent CF -He mixture are quite close to the corresponding valuesfor air, deviating therefrom by less than about i 12 percent. It isevident, therefore, that respiration and voice communication inatmospheres based on this mixture should be essentially the same as inair, although turbulent flow in breathing passages will give highereffective viscosities for a mix containing CF The thermal conductivityof the 30-70 percent CF He mixture, while about 2% times that in air, isstill below one half the thermal conductivity of helium. Loss of bodilyheat, therefore, is evidently less severe than in helium. The additionof a suitable partial pressure of oxygen to the CF -He mixture tends tobring most of the pertinent properties of the mixture closer to those ofair.

In the tests on white mice, the mice were placed in an atmosphere ofpure oxygen at 14.7 p.s.i.a. and compressed at a rate of about 30p.s.i.a. per minute with the test auxiliary gas to a final totalpressure of the auxiliary gas of about 150 p.s.i.a., at which resultingpressure the mice were maintained for about one hour. Decompression wascarried out over a period of about an hour and a quarter withintermittent addition of oxygen. All the mice tested surviveddecompression and appeared normal during several days subsequentobservation. The mice were tested singly and in pairs. Soda-limecanisters were provided for absorption of metabolic carbon dioxide.

Breathing tests were also made on human subjects at ordinary atmosphericpressure. A mixture of 80 percent by volume of carbon tetrafluoride andpercent by volume of oxygen was observed to lower the apparent pitch ofthe voice somewhat, but it did not impair the intelligibility of thespeech. A mixture 80 parts by volume of a mixture of volume percentcarbon tetrafluoride and 70 volume percent helium, with 20 parts byvolume of oxygen caused no noticeable change in speech. Most subjectsreported these mixtures to be odorless and tasteless and none found themto be objectionable.

While in the preferred mixtures disclosed herein helium is used as thesecond inert gas to be mixed with the oxygen and carbon tetrafluoride,it is to be understood that the invention is not restricted to the useof helium for this purpose. lnert or auxiliary gases which may be usedinclude nitrogen, helium, neon, argon, hydrogen, etc., or anycombination of these, even though the use of some of these gases may beless advantageous than the use of helium, and it is to be understoodthat the use of carbon tetrafluoride as the sole inert gas in abreathing mixture is also covered by the invention.

While illustrative compositions of matter in accordance with theinvention have been described and specified herein, it will beunderstood that numerous changes may be made without departing from thegeneral principles and scope of the invention.

We claim:

I. A hyperbaric breathing mixture for a hyperbaric environmentconsisting essentially of oxygen at a partial pressure not less thanabout two pounds per square inch absolute and not more than about twoatmospheres and an inert component consisting essentially of helium andcarbon tetrafluoride in which the volumetric proportions of the heliumand carbon tetrafluoride are approximately 70 volume percent and 30volume percent respectively, said inert component at such partialpressure as to provide a breathing mixture having a total pressuresufficient to sustain breathing in the hyperbaric environment.

